Advances in HIV/AIDS Research

Search for HIV Vaccine Gets a Shot in the Arm

Laboratories at the Armed Forces Research Institute of Medical Sciences in Bangkok, Thailand.
Credit: U.S. Military HIV Research ProgramView Larger Image

Scientists have been striving for a safe and effective vaccine to prevent
HIV infection ever since the virus was identified in 1984. The first signal
that such a vaccine is possible came in September 2009 from a clinical trial
funded in large part by the National Institute of Allergy and Infectious
Diseases (NIAID). With more than 16,000 adult participants in Thailand,
the trial showed that an investigational vaccine regimen was safe and 31
percent effective at preventing HIV infection.

The vaccine regimen consisted of two separate vaccines. The first was
a killed canarypox virus containing pieces of HIV DNA, and the second was
an HIV surface protein that plays a key role in infection. This regimen
was based on HIV strains that commonly circulate in Thailand. The main goal
of the vaccine regimen was to train the immune system to attack HIV, so
that if a vaccinated individual were exposed to the virus, his or her immune
system would successfully fight off the infection. A secondary goal was
to determine if the vaccine regimen could reduce the amount of HIV in the
blood of vaccinated study participants who later became infected with the
virus.

Conducted in the Rayong and Chon Buri provinces of Thailand, the trial
enrolled more than 16,000 men and women ages 18 to 30 years old at various
levels of risk for HIV infection. Participants received either the vaccine
regimen or a placebo and were tested for HIV infection every 6 months for
3 years. During each clinic visit, the participants were counseled on how
to avoid becoming infected with HIV.

Vials of VAC-HIV
Credit: U.S. Military HIV Research Program

Led by the Thai Ministry of Public Health’s Department of
Disease Control, the study was sponsored by the U.S. Army in collaboration
with NIAID, Sanofi Pasteur and Global Solutions for Infectious
Diseases.

In the final analysis, 74 of 8,198 placebo recipients became infected
with HIV compared with 51 of 8,197 participants who received the
vaccine regimen. This difference in the number of people who became
infected was statistically significant, meaning it is unlikely
the study results were due to chance. The vaccine regimen did not
reduce the amount of virus in the blood of people who became infected
with HIV.

NIAID and its partners in this study are now working with other
scientific experts to understand how the vaccine regimen in the
Thai trial protected some participants from HIV infection, with
the hope of using that knowledge to create a more effective HIV
vaccine.